Cadmium - Cd
Pieces of very pure cadmium metal, which are covered by a thin layer of oxide. This makes the metal appear grey and dull. Some of the uncovered metal still can be seen as silvery spots with a slight yellow cast, but in contact with air, these shiny spots soon also will be covered by a grey layer. Once the metal is covered by the oxide layer, it will not corrode further.
The picture below shows a sample of very pure cadmium metal, from which the oxide layer was removed. This picture shows the nice silvery color of the metal with a very slight yellow cast.